A tubeless pneumatic tire is lined with an air-permeation preventing layer in an integrated manner. A butyl rubber which exhibits excellent air non-permeability is used as a material for the air-permeation preventing layer. Because, however, the butyl rubber has a large specific gravity, the butyl rubber places obstacles in the way of manufacturing lighter-weight pneumatic tires, which is an increasingly strong demand from the market in these years. As measures to meet the demand, Patent Document 1 has proposed use of a thermoplastic resin film, instead of the butyl rubber, as an air-permeation preventing layer, with a smaller specific gravity of the thermoplastic resin film taken into consideration, thereby paving the way for manufacturing pneumatic tires with a far lighter weight.
However, the use of the thermoplastic resin film as the air-permeation preventing layer comes with a problem that blisters are easy to occur inside a tire during a vulcanization molding step. As shown in FIG. 2, a pre-vulcanized green tire is formed by placing a cylindrical thermoplastic resin film 6 around a making drum 20, and subsequently laminating a carcass material onto the thermoplastic resin film 6 with an unvulcanized rubber sheet material 7 such as a tie rubber being interposed in between. The rubber sheet material 7 includes a spliced part 11, which is step-shaped, and which is formed when one end portion of the rubber sheet material 7 is spliced onto the other end portion thereof after the rubber sheet material 7 is wound around the thermoplastic resin film 6. An air pocket 10 which has a triangular cross-section is formed between the step of this spliced part 11 and the thermoplastic resin film 6, as shown in FIG. 7(A). When the green tire is formed by further laminating the other tire members such as a belt layer and a tread rubber onto the resultant rubber sheet material 7 under the presence of such air pocket 10, and then is molded through vulcanization, the air contained in the air pocket 10 increases in volume. Then, a part of the surface of the thermoplastic resin film 6 accordingly rises, as shown in FIG. 7(B). In other words, a blister 13 is formed. The blister 13 not only damages an aesthetic outer appearance of the inner surface of the tire, but also often poses a cause of breakage of the thermoplastic resin film while in use.
Because, as described above, the blister is caused by the volume increase of the air pocket during vulcanization molding, the blister conspicuously appears when the air pocket grows large. As long as the air pocket is small, no blister takes place.
Specifically, the blister is easier to take place as the step of the spliced part becomes larger when the rubber sheet material 7 is 0.5 mm or more in thickness.
On the other hand, rubber materials including the butyl rubber cause no blister to take place, because a property of the rubber materials is air absorption. Even when, as described above, an air pocket is formed, by using one of the rubber materials as the air-permeation preventing layer, the air in the air pocket is eventually absorbed in the rubber material during vulcanization. In sum, the blister is a problem peculiar to a case when the thermoplastic resin film is used as the air-permeation preventing layer.    Patent Document 1: Japanese patent application Kokai publication No. Hei. 8-258506